1. Field of the Invention
The present invention relates to keyless entry systems generally and, more particularly, but not by way of limitation, to a novel method of recovering synchronization between a transmitter and a receiver of a keyless entry system.
2. Background Art
Current remote keyless entry systems that employ rolling code algorithms occasionally require resynchronization of receiver to transmitter. For instance, changing the transmitter battery, occurrence of a noise spike when writing to receiver's EEPROM, or when pressing the transmitter button(s) too many times while outside the range of the receiver may cause the system to lose synchronization. Once synchronization is lost, the system does not respond and appears inoperative. Resynchronization is required to restore the system operation to normal. Current systems require a manual sequence of operations for restoring synchronization, such as depressing lock and unlock buttons for a predetermined period of time and waiting for a lock cycle feedback. This manual operation can be confusing, and if the operator does not know the procedure, the operator may bring the keyless entry system in for service. This leads to customer dissatisfaction and high warranty cost for toe manufacturer, e.g., a vehicle manufacture.
One method to eliminate the manual resynchronization is by using non-volatile memory in the transmitter. In this circumstance it is assumed that the transmitter sequence number will never be below the receiver's sequence mumber, and therefore manual resynchronization would not be required. A further assumption is that data written and stored in the transmitter's EEPROM will always be valid. However, this method comes with many shortfalls. One is cost. EEPROM is relatively expensive, and packaging external EEPROM in the transmitter can be difficult, if not impossible, on some applications requiring minimum layout area. With EEPROM, complex program routines are required to guarantee that the data written is truly valid, otherwise complete reprogramming of the system will be necessary to recover normal operation. This is time consuming and is a great inconvenience to the end user. The factors of cost, packaging, EEPROM reliability, and increase in code size dictate that using EEPROM in the transmitter is not a reliable nor viable method for keeping the system in synchronization. What is needed, but heretofore has been unavailable, is a method whereby resynchronization is activated intuitively by, and transparently to, the operator. Such a method should also permit that the entire resynchronization process be implemented only in the receiver without need for the transmitter to store any special resynchronization commands, nor execute any special program routines to recover synchronization. Additionally, a method is needed whereby the authorized user is not expected to learn any complicated resynchronization procedures.
Accordingly, it is a principal object of the present invention to provide a method for restoring synchronization between a transmitter and receiver without the use of special manual resynchronization procedures.
A further object of the present invention is to reduce costs by eliminating EEPROM in the transmitter.
An additional object of the present invention is to reduce the RF design of the transmitter by eliminating external EEPROM in the transmitter.
It is yet a further object of the present invention to eliminate special EEPROM validation program routines in the transmitter and receiver.
It is yet an additional object of the present invention to maintain the security level between transmitter and receiver.
It is yet another object of the present invention to provide more packaging flexibility of the system by eliminating the need for external EEPROM in the transmitter.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.